According to sleep expert Dr.Robert Schacher,many people have difficult sleeping, but they do not know why.Most people know it is important not to drink coffee or tea before they go to bad-both beverages have caffeine.Caffeine keeps people awake.However,not everybody knows that some medicines,such as cold tablets,also have caffeine in tham. stress can cause insomnia,too. Busy people with stressful jobs may not be able to sleep at night.